Historically, it has been recognized, especially in actuation of the control surfaces of aircraft or linkages thereto, that should a jam occur anywhere in the actuation path, the power delivered to the jammed linkages or control surfaces could result in serious damage to the aircraft structure or the flight control surfaces themselves.
The developers of recirculating ball and screw type actuators have long recognized that overloading of the actuator may occur when excessive loads are encountered. In order to prevent damage to the actuator or to the apparatus being operated, many load absorbing mechanisms have been produced. Typical of this effort is the arrangement shown in the Clarke U.S. Pat. No. 3,802,281. The Clarke patent discloses a driving arrangement for a lead screw 21 mounted for reciprocation in a recirculating ball nut assembly 18. The nut assembly 18 is, in turn, mounted in a tubular drive member 14 that has integral, therewith, a spur gear 17 which is drivingly connected to a bevel gear arrangement 11, 12. Power is delivered through the bevel gear arrangement 11, 12 to the actuator. The drive member 14 is resiliently coupled to the nut 18 so as to be rotatable relative to the nut member 18 at a predetermined torque load. A brake in the form of rollers 31 jammed against the actuator body 10 operates in response to the aforementioned relative rotation. A flange 33 on nut 18 cooperates with friction pad 35 to brake the rotary motion of the nut when an axial load is applied to the lead screw. The invention to be described hereinafter does away with the requirement that the nut portion of the assembly senses the presence of the excess load. The instant invention depends only on the detection of excessive axial loading present in the actuator screw.